The invention described herein is a direct development of the one that is fully described in the co-pending application, Ser. No. 631,409, of Mark Edward Whalen, now U.S. Pat. No. 4,067,096, issued Jan. 10, 1978. Rather than repeat its contents here, it is the inventor's intention that the disclosure thereof be directly consulted for all of its contents, by any concerned person, just as if such had been set forth in extenso here.
In the closest other precursors of the present invention known to the inventor, the resulting billet is either (a) less than fully dense, throughout, including the outer peripheral surface thereof, so it is vulnerable and subject to corrosion, or (b) it is fully dense throughout. According to the present inventor's view, in the latter instance the additional heat and/or pressure required to fully densify the product is a waste of energy.
The prior art processes in which scrap fragments are loaded into a pre-formed shell (called a "coffin" in the art) for pressing and/or heating to form a "billet" seem most likely to produce a product most similar to that provided by use of the process of the present invention. However, that is not the case. In fact, in those processes, the fully dense layer only partially peripherally surrounds the core and/or the core is not sufficiently centralized as to avoid problems should one try to roll the resulting "billet" into sheet. In the latter case, because some voids remain near the lateral margins, they may pop open during rolling. The resulting uneven edges of the strip will catch in side guides of the rolling mill and cause the strip to cobble.
The above-mentioned co-pending application describes a process wherein:
(a) heating is accomplished at least largely by electrical induction of a metal scrap stream that is so low-density that its outside gets hot enough to weld long before the inside gets that hot, and PA1 (b) heating and pressing are carried out sufficiently to seal the outer peripheral surface of the "billet", but not significantly more heat and pressure are wasted to make the billet fully solid at this stage.
In seeking to put that invention into commercial practice, a practical problem has been encountered. It is necessary to laterally confine the columnar stream of scrap particles during the induction heating step, because it is so much below full density.
As in many such processes, there is a trade-off between pressure and temperature. The higher the temperature to which the scrap is heated, the lower will be the minimum pressure needed to consolidate the heated scrap into the desired product. Conversely, the lower the temperature to which the scrap is heated, the greater will be the minimum pressure needed to consolidate the heated scrap into the desired product.
A typical wall material that is available is non-magnetic stainless steel, as it is not inductively heated.
At a temperature of about 1980.degree. F., the non-magnetic stainless steel gets "tacky" and begins to tentatively weld to the scrap column.
That provides a temperature constraint on conducting the process, and may necessitate the use of uneconomically sturdy pressure applying means and unacceptably great force application to be commercially practicable.